1. Field of the Invention
This invention relates to a method and system for transmitting audio signals over a dedicated video signal line, and particularly relates to a simple and inexpensive method and system for transmitting analog audio signals over a dedicated video line within the normal video area of the NTSC or PAL/SECAM signal.
2. Description of the Prior Art
Methods and systems for transmitting audio signals over dedicated video signal lines are in existence. However, presently existing systems use parallel (additional) audio channel or a digital technique to transmit digital audio signals within the various synchronizing signals of the video picture signal. As examples, the invention of U.S. Pat. No. 5,842,171 teaches the encoding of digital audio into a SMPTE digitized video signal as a burst of digital data that fits into a specified time slot of the SMPTE standard. The invention of U.S. Pat. No. 5,929,922 teaches the sending of digital audio inside television vertical blanking intervals. The invention of U.S. Pat. No. 5,940,070 refers to a method of sending digitized audio over one of the video lines of a standard VGA display system, with synchronization data coming over a separate line. Each of these systems requires digital-to-analog (DTA) converters and analog-to-digital (ATD) converters in order to convert the particular audio signal into a useable format, and one requires an additional transmission line. In addition, while inserting additional information into the video signals during the video blanking periods is well known, this technique typically violates the TV video signal standard, frequently resulting in visible retraces on the video screen.
It is therefore desirable to provide a simple method and apparatus for sending audio signals along a line dedicated to video without the need for either a separate communication line, or the need for cumbersome DTA/ATD converters and buffering systems at either end of the line.
The present invention provides a method and apparatus for transmission of analog audio signals over a dedicated video communication line, wherein the analog audio signal is inserted into and becomes a part of the video signal. The analog audio signal can be inserted into a defined amount of active video interval (bandwidth) reserved from the active video line, either at the beginnings or endings of the active video line scan signal, or at both the beginnings and endings of the video line scan signal for transmission of two audio signals (e.g., for stereo audio, or for bi-directional (duplex) audio communication in closed circuit television (CCTV) applications). A defined amount of active video interval (bandwidth) is reserved from the active video line, and is replaced with samples of the analog audio signal. The analog audio signal samples are inserted at either the beginnings or endings, or both, of the active video line scan signal, because the beginnings and endings of the active video ordinarily occur outside the actual boundaries of the video picture, i.e., within the vertical black borders of the video screen which in most cases will be undetected due to the common practice of allowing the monitors to overscan.
It is therefore a primary object of the present invention to provide a method and apparatus for transmitting an analog audio signal as part of the active video line scan signal through a single communication line.
It is also an important object of the present invention to provide a method and apparatus for inserting samples of an analog audio signal at either the beginnings or the endings of each active video line scan signal transmitted through a single communication line.
It is also an important object of the present invention to provide a method and apparatus for transmitting a pair of audio signals as part of the active video line scan signal through a single communication line.
It is also an important object of the present invention to provide a method and apparatus for inserting samples of a pair of analog audio signals as part of the active video line scan signal, one set of audio signal samples at the beginnings, and the other set of audio signal samples at the endings of each active video line scan signal transmitted through a single communication line.
Additional objects of the invention will be apparent from the detailed descriptions and the claims herein.